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Question
Assertion :Alveoli are the primary sites for exchange of gases. Reason: All factors in our body are favourable for the diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli.
Assertion :Alveoli are the primary sites for exchange of gases. Reason: All factors in our body are favourable for the diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli.
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Solution
The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
The solubility of the gases, as well as the thickness of the membranes involved in diffusion, are important factors that affect the rate of diffusion. A gradient of partial pressure is present for oxygen from alveoli to blood and blood to tissue. Similarly, a gradient of CO2 is present in the opposite direction i.e., from tissues to blood and blood to alveoli. It is further dependent on the solubility of the diffusing gases. As the solubility of CO2 is 20-25 times higher than that of O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2. Therefore, all the factors in our body are favourable for diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli. The alveolus is the primary site of exchange as it has an extensive network of blood capillaries and consists of squamous epithelium. Due to the very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily.So the correct answer is 'Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion'.
The solubility of the gases, as well as the thickness of the membranes involved in diffusion, are important factors that affect the rate of diffusion. A gradient of partial pressure is present for oxygen from alveoli to blood and blood to tissue. Similarly, a gradient of CO2 is present in the opposite direction i.e., from tissues to blood and blood to alveoli. It is further dependent on the solubility of the diffusing gases. As the solubility of CO2 is 20-25 times higher than that of O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2. Therefore, all the factors in our body are favourable for diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli. The alveolus is the primary site of exchange as it has an extensive network of blood capillaries and consists of squamous epithelium. Due to the very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily.
So the correct answer is 'Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion'.
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